linux-kernel - Re: [PATCH v6 15/25] KVM: x86: Add fault checks for guest CR4.CET setting

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Message-ID: <fcc76a837a5f5eb4ed57b298a455694106d5c9c7.camel@redhat.com>
Date:   Tue, 31 Oct 2023 19:51:57 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...el.com, peterz@...radead.org, chao.gao@...el.com,
        rick.p.edgecombe@...el.com, john.allen@....com
Subject: Re: [PATCH v6 15/25] KVM: x86: Add fault checks for guest CR4.CET
 setting

On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> Check potential faults for CR4.CET setting per Intel SDM requirements.
> CET can be enabled if and only if CR0.WP == 1, i.e. setting CR4.CET ==
> 1 faults if CR0.WP == 0 and setting CR0.WP == 0 fails if CR4.CET == 1.
> 
> Reviewed-by: Chao Gao <chao.gao@...el.com>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/x86.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a091764bf1d2..dda9c7141ea1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1006,6 +1006,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>  	    (is_64_bit_mode(vcpu) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PCIDE)))
>  		return 1;
>  
> +	if (!(cr0 & X86_CR0_WP) && kvm_is_cr4_bit_set(vcpu, X86_CR4_CET))
> +		return 1;
> +
>  	static_call(kvm_x86_set_cr0)(vcpu, cr0);
>  
>  	kvm_post_set_cr0(vcpu, old_cr0, cr0);
> @@ -1217,6 +1220,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  			return 1;
>  	}
>  
> +	if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
> +		return 1;
> +
>  	static_call(kvm_x86_set_cr4)(vcpu, cr4);
>  
>  	kvm_post_set_cr4(vcpu, old_cr4, cr4);

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky